A sensor, also called a detector, is a device that measures a physical quantity and converts it to a signal which may be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which may be read on a calibrated glass tube. A thermocouple converts temperature to an output voltage which may be read by a voltmeter. For accuracy, most sensors are calibrated against known standards.
Sensors may be used in chemical and biochemical testing to determine characteristics of an analyte of interest within a specimen or sample. In biomedicine and biotechnology, sensors which detect analytes having a biological component, such as cells, protein, or nucleic acid are called biosensors. Biosensors may be used for both in vitro and in vivo applications. In other fields of chemistry sensors may detect analytes having predetermined chemical compositions or chemical components. For example conductometric sensors may take conductivity measurements to measure hematocrit. In another example, ion selective electrodes may be used for biological and non-biological samples, such as testing for predetermined ions in water samples, for example. Sensors of these and other similar types may be used for industrial testing, agriculture, food testing, bioweapons testing, and drug use testing, for example.
Sensors may be exposed to a sample, such as blood, urine, interstitial fluid, body fluid specimens, organic chemical compounds, inorganic chemical compounds, and other samples having analytes of interest, and used to detect predetermined analytes within the sample. The sensor may then be exposed to a transducer or detector element which may work in a physiochemical manner using a sensing medium such as light, electricity, piezoelectric, electrochemical, or the like. In any event, the transducer or detector element transforms a signal from the sensor into another signal that may be more easily measured and quantified. The signal produced by the transducer or detector element may be provided to a reader device having associated electronics, signal processors, and/or a display to provide the results in a user readable format. For example, the results may be provided on a graphical display.
Test strips are widely used in the fields of clinical chemistry, biochemistry, and the medical field, among other industries. Test strips may have single or multiple sensors connected to the strip. Regardless of the amount of sensors, test strips are often single use tests which, once used, are discarded. Common examples of test strips are glucose strips and urine test strips. Some sensors, used in test strips, may undergo a color change in response to contact with a sample. For example, urine test strips often use color change sensors. Reagent test strips are widely used in the field of clinical chemistry and employ color changing sensors. A test strip usually has one or more test areas, also called reagent pads, and each test area is capable of undergoing a color change in response to contact with a liquid specimen, such as a biological or chemical sample. The liquid sample usually contains one or more analytes of interest. The presence and concentrations of these analytes of interest in the sample are determinable by an analysis of the color changes undergone by the reagent pads. Usually, this analysis involves a color comparison between the reagent pad and a color standard or scale. A reflectance spectroscope is commonly used to analyze analytes of interest applied to the reagent pads. A conventional spectrophotometer determines the color of a sample applied to one or more of the reagent pads disposed on a white, non-reactive surface by illuminating the pad and taking a number of reflectance readings from the pad, each having a magnitude relating to a different wavelength of visible light. Today, strip reading instruments employ a variety of area array detection readheads utilizing CCD (charge-coupled device), CID (charge-injection device) or PMOS detection structures for detecting color changes to the reagent pads. The color of the sample on the pad may then be determined based upon the relative magnitudes of red, green and blue reflectance signals.
Conventional spectrophotometers may be used, for example, to perform a number of different urinalysis tests utilizing a reagent strip on which a number of different reagent pads are disposed. Each reagent pad is provided with a different reagent which causes a color change in response to the presence of a certain type of constituent in a sample such as leukocytes (white blood cells), red blood cells, glucose, bilirubin, urobilinogen, nitrite, protein, ketone bodies, or other analytes of interest. The color developed in a particular analyte defines the characteristic discrete spectrum for absorption of light for that particular analyte. For example, the characteristic absorption spectrum for color-developed glucose falls within the upper end of the blue spectrum and the lower end of the green spectrum. Reagent strips may have ten different types of reagent pads.
Other optical readers are known that do not use reflectance, but rather capture an image of the test strips and convert the captured signal to RGB or to another format from which the color of the reagent pads on the test strip can be determined. See for example, U.S. Pat. No. 5,408,535, which is also assigned to the assignee of the present disclosure and is incorporated herein by reference in its entirety. These optical readers can also be used to read slides or other diagnostic tests.
Optical readers may be incorporated into automated instruments which read test strips or continuous testing material. The CLINITEK ATLAS automated urinalysis system, which is manufactured and sold by Siemens Healthcare Diagnostics, uses a cassette containing reagent areas mounted seriatim on a continuous plastic substrate which is wound into a reel rotatably housed in the cassette. Another continuous testing material is disclosed in U.S. Pat. No. 7,927,545.
Other sensors include conductometric sensors, electrochemical sensors, and amperometric sensors. Conductometric sensors or chemiresistors may operate on an impedance principle and be used to detect compounds such as hematocrit, for example. Conductometric sensors may operate by applying a material capable of changing its conductivity upon interaction with the analyte of interest. The material is placed between and in contact with two contact electrodes and the resistance of the electrodes and the material is measured. Conductometric sensors may also have the material layered atop an electrode and be provided with a counter-electrode to complete a circuit. Electrochemical sensors may be implemented as ion selective electrodes or potentiometric sensors which may measure values for pH, Na+, Ca+, K+, Cl−, or other ions, for example. Potentiometric sensors may operate by measuring a signal as a potential difference between a working electrode and a reference electrode where the potential of the working electrode is based on a concentration of the analyte of interest and the reference electrode provides a defined reference potential. Amperometric sensors may analyze samples for compounds such as enzymatic lactate, glucose, and creatinine, for example. Amperometric sensors may operate by passing a voltage potential between two electrodes positioned within a sample and measuring the current changes as an analyte of interest is oxidized at an anode electrode or reduced at a cathode electrode. The potential applied to the electrodes may be adjusted to tailor a response to a predetermined analyte of interest.
An interdigitated sensor array may be provided with at least two microelectrodes, both of which have fingers which are spaced apart and interleaved in an interdigitated fashion. Each of the microelectrodes is provided with a relatively large trace connected to a plurality of relatively fine traces. In biomedicine and biotechnology, the amount of analytes of interest within a sample is very small and difficult to detect. As such, amplification of the signal provides more accurate reading for a detected analyte.
Typically test strips or cartridges of the types described above are single use tests. These tests present issues of inventory management, where a user must store and track inventory in a centralized area to serve multiple single use test instruments. Included in the issue of inventory management, real time inventory may be of increased importance to determine when inventory of single use tests are low. Of note, is that there is no guarantee that all sensors within a lot of test strips have been stored in comparative conditions potentially leading to erroneous readings on test strips due to certain test strips within a lot being stored in differing ambient conditions. If a single use test strip fails, a sample may be lost and a user may be required to locate another test strip stored in appropriate conditions to retest a new sample. There exists a need for a multi-single use testing material and testing instrument which may streamline concerns of inventory, batch storage with regards to controlled or known conditions, instrument based inventory management, and similarity in treatment of sensors within a lot.